Discrete Polymer in Fan-Out Packages

ABSTRACT

A package includes a first molding material, a lower-level device die in the first molding material, a dielectric layer over the lower-level device die and the first molding material, and a plurality of redistribution lines extending into the first dielectric layer to electrically couple to the lower-level device die. The package further includes an upper-level device die over the dielectric layer, and a second molding material molding the upper-level device die therein. A bottom surface of a portion of the second molding material contacts a top surface of the first molding material.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/830,458, entitled “Discrete Polymer in Fan-Out Packages,” filed onDec. 4, 2017 which is a continuation of U.S. patent application Ser. No.15/431,192, entitled “Discrete Polymer in Fan-Out Packages,” filed onFeb. 13, 2017, now U.S. Pat. No. 9,837,379 issued Dec. 5, 2017, which isa divisional of U.S. patent application Ser. No. 14/690,081, entitled“Discrete Polymer in Fan-Out Packages,” filed on Apr. 17, 2015, now U.S.Pat. No. 9,666,502 issued May 30, 2017, which applications areincorporated herein by reference.

BACKGROUND

With the evolving of semiconductor technologies, semiconductor dies arebecoming increasingly smaller. More functions, however, need to beintegrated into the semiconductor dies. Accordingly, the semiconductordies need to have increasingly greater numbers of Input/output (I/O)pads packaged into smaller areas, and the density of the I/O pads risesquickly. As a result, the packaging of the semiconductor dies becomesmore difficult, and adversely affecting the yield.

Package technologies can be divided into two categories. One category istypically referred to as Wafer Level Package (WLP), wherein the dies ona wafer are packaged before they are sawed. The WLP technology has someadvantageous features, such as a greater throughput and a lower cost.Further, less underfill or molding compound is needed. However, the WLPtechnology suffers from drawbacks. The conventional WLP can only befan-in type packages, in which the I/O pads of each die are limited to aregion directly over the surface of the respective die. With the limitedareas of the dies, the number of the I/O pads is limited due to thelimitation of the pitch of the I/O pads. If the pitch of the pads is tobe decreased, solder bridging may occur. Additionally, under the fixedball-size requirement, solder balls must have a certain size, which inturn limits the number of solder balls that can be packed on the surfaceof a die.

In the other category of packaging, dies are sawed from wafers beforethey are packaged onto other wafers, and only “known-good-dies” arepackaged. An advantageous feature of this packaging technology is thepossibility of forming fan-out packages, which means the I/O pads on adie can be redistributed to a greater area than the die itself, andhence the number of I/O pads packed on the surfaces of the dies can beincreased.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 through 11 illustrate the cross-sectional views of intermediatestages in the formation of a multi-stacking fan-out package inaccordance with some embodiments;

FIG. 12 illustrates a top view of a portion of the multi-stackingfan-out package;

FIG. 13 illustrates a magnified view of a portion of a multi-stackingfan-out package in accordance with some embodiments;

FIGS. 14 through 16 illustrate the cross-sectional views of intermediatestages in the formation of a multi-stacking fan-out package inaccordance with alternative embodiments, wherein no opening is formed inupper polymer layers;

FIGS. 17 and 18 illustrate the cross-sectional views of intermediatestages in the formation of a multi-stacking fan-out package inaccordance with alternative embodiments, wherein a liquid moldingcompound is applied;

FIGS. 19 through 21 illustrate the cross-sectional views of intermediatestages in the formation of a multi-stacking fan-out package inaccordance with alternative embodiments, wherein a partial cut isperformed prior to applying a liquid molding compound; and

FIG. 22 illustrates a process flow for forming a multi-stacking fan-outpackage in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

A multi-stacking fan-out packages and the method of forming the same areprovided in accordance with various exemplary embodiments. Theintermediate stages of forming the multi-stacking fan-out packages areillustrated. The variations of the embodiments are discussed. Throughoutthe various views and illustrative embodiments, like reference numbersare used to designate like elements.

FIGS. 1 through 11 illustrate the cross-sectional views of intermediatestages in the formation of a multi-stacking fan-out package inaccordance with some embodiments of the present disclosure. In thesubsequent discussion, the process steps shown in FIGS. 1 through 11 arediscussed referring to the process steps in FIG. 12.

Referring to FIG. 1, carrier 30 is provided, and adhesive layer 32 isdisposed over carrier 30. Carrier 30 may be a blank glass carrier, ablank ceramic carrier, or the like, and may have a shape of asemiconductor wafer with a round top-view shape. Carrier 30 is sometimesreferred to as a carrier wafer. Adhesive layer 32 may be formed of aLight-to-Heat Conversion (LTHC) material, for example, and other typesof adhesives may also be used. In accordance with some embodiments ofthe present disclosure, adhesive layer 32 is capable of decomposingunder the heat of light, and hence can release carrier 30 from thestructure formed thereon.

Buffer layer 34 is formed over adhesive layer 32. In accordance withsome embodiments of the present disclosure, buffer layer 34 is a polymerlayer formed of polybenzoxazole (PBO), polyimide, or the like.

Device dies 36 are placed over buffer layer 34. The respective step isshown as step 202 in the process flow shown in FIG. 22. Device dies 36may be adhered to buffer layer 34 through die attach films 38. The edgesof die attach films 38 are co-terminus with (aligned to) the edges ofthe respective overlaying device dies 36. Die attach films 38 areadhesive films. The plurality of placed device dies 36 may be arrangedas an array including a plurality of rows and a plurality of columns.Device dies 36 may include a semiconductor substrate having a backsurface (the surface facing down) in contact with the respective dieattach films 38. Device dies 36 further include integrated circuitdevices (such as active devices, which include transistors, for example,not shown) at the front surfaces (the surface facing up) of thesemiconductor substrates. Device dies 36 may include memory dies such asStatic Random Access Memory (SRAM) dies, Dynamic Random Access Memory(DRAM) dies, or the like.

Device dies 36 include conductive features such as metal pillars 40 attheir top surfaces. Metal pillars 40 are electrically coupled to theintegrated circuits inside device dies 36. In accordance with someexemplary embodiments of the present disclosure, as shown in FIG. 1, thetop surfaces of metal pillars 40 are exposed. Metal pillars 40 may becopper pillars, and may also include other conductive/metallic materialssuch as aluminum, nickel, or the like. In accordance with someembodiments of the present disclosure, the top surfaces of metal pillars40 are coplanar with the top surface of dielectric layer 42. Inaccordance with alternative embodiments of the present disclosure, metalpillars 40 are embedded in dielectric layer 42, with the top surfaces ofdielectric layers 42 being higher than the top surfaces of metal pillars40. Dielectric layer 42 may be formed of a polymer, which may includePBO, polyimide, or the like. Throughout the description, device dies 36are also referred to as level-1 dies or lower-level dies.

Referring to FIG. 2, molding material 44 is molded on device dies 36.The respective step is shown as step 204 in the process flow shown inFIG. 22. Throughout the description, the “molding material” isalternatively referred to as “encapsulating material,” and the step of“molding” is alternatively referred to as “encapsulating.” Moldingmaterial 44 is dispensed as a fluid and is then cured, for example, in athermal curing process. Molding material 44 fills the gaps betweendevice dies 36 and may be in contact with buffer layer 34. Moldingmaterial 44 may include a molding compound, a molding underfill, anepoxy, or a resin. After the molding process, the top surface of moldingmaterial 44 is higher than the top ends of metal pillars 40.

Next, a planarization step such as a Chemical Mechanical Polish (CMP)step or a grinding step is performed to planarize molding material 44,until metal pillars 40 of device dies 36 are exposed. The respectivestep is shown as step 206 in the process flow shown in FIG. 22. Theresulting structure is shown in FIG. 3. Due to the planarization, thetop surfaces of metal pillars 40 are substantially level (coplanar) withthe top surface of molding material 44.

Referring to FIG. 4, one or more layers of dielectric layers 46 and therespective Redistribution Lines (RDLs) 48 are formed over moldingmaterial 44 and metal pillars 40. The respective step is shown as step208 in the process flow shown in FIG. 22. In accordance with someembodiments of the present disclosure, dielectric layers 46 are formedof a polymer(s) such as PBO, polyimide, or the like. In accordance withalternative embodiments of the present disclosure, dielectric layers 46are formed of an inorganic dielectric material(s) such as siliconnitride, silicon oxide, silicon oxynitride, or the like.

RDLs 48 are formed to electrically couple to metal pillars 40. RDLs 48may include metal traces (metal lines) and vias underlying and connectedto the respective metal traces. In accordance with some embodiments ofthe present disclosure, RDLs 48 are formed through plating processes,wherein each of RDLs 48 includes a seed layer (not shown) and a platedmetallic material over the seed layer. The seed layer and the platedmetallic material may be formed of the same material or differentmaterials.

During the formation of RDLs 48, dielectric layers 46 are patterned toform via openings (occupied by RDLs 48), and upper-level RDLs 48 extendinto the via openings to contact lower-level RDLs 48 or metal pillars40. At the same time the via openings are formed, some portions ofdielectric layers 46 are also removed to form openings 49 in dielectriclayers 46. The formation of via openings and openings 49 may beperformed using a same lithography mask and same lithography processes.Openings 49 may form a grid including horizontal openings (trenches,viewed from top) crossing vertical openings. The remaining portions ofdielectric layers 46 are thus in the regions defined by the grid.

Referring to FIG. 5, metal posts 50 are formed over dielectric layers46, and are electrically connected to RDLs 48. Throughout thedescription, metal posts 50 are alternatively referred to asthrough-vias 50 since metal posts 50 penetrate through the subsequentlyformed molding material. The respective step is shown as step 210 in theprocess flow shown in FIG. 22. Through-vias 50 are connected to RDLs 48through the vias formed in the top layer of dielectric layers 46. Inaccordance with some embodiments of the present disclosure, through-vias50 are formed by plating, and the formation process may includepatterning the top layer of dielectric layers 46 to form openings toexpose RDLs 48, forming a blanket seed layer (not shown) extending intothe openings, forming and patterning a photo resist (not shown), andplating through-vias 50 on the portions of the seed layer that areexposed through the openings in the photo resist. The photo resist andthe portions of the seed layer that were covered by the removed photoresist are then removed. The material of through-vias 50 may includecopper, aluminum, nickel, tungsten, or the like. Through-vias 50 havethe shape of rods. The top-view shapes of through-vias 50 may becircles, rectangles, squares, hexagons, or the like.

FIG. 6 illustrates the placement of device dies 52 over dielectriclayers 46. Throughout the description, device dies 52 are also referredto as level-2 dies or upper-level dies. The respective step is shown asstep 212 in the process flow shown in FIG. 22. Device dies 52 may beadhered to the top dielectric layer 46 through die attach films 54,which are adhesive films. Each of device dies 52 may include asemiconductor substrate having a back surface (the surface facing down)in physical contact with the respective die attach film 54. Device dies52 further includes integrated circuit devices (such as active devices,which include transistors, for example, not shown) at the front surface(the surface facing up) of the semiconductor substrate. Device dies 52may include logic dies such as Central Processing Unit (CPU) dies,Graphic Processing Unit (GPU) dies, mobile application dies, or thelike. Device dies 52 may also include System on Chip (SoC) dies.

Device dies 52 include conductive features such as metal pillars 56 attheir top surfaces. Metal pillars 56 are electrically coupled to theintegrated circuits inside device dies 52. In accordance with someexemplary embodiments of the present disclosure, as shown in FIG. 6, thetop surfaces of metal pillars 56 are exposed. Metal pillars 56 may becopper pillars, and may also include other conductive/metallic materialssuch as aluminum, nickel, or the like. In accordance with someembodiments of the present disclosure, the top surfaces of metal pillars56 are coplanar with the top surface of dielectric layer 58. Inaccordance with alternative embodiments of the present disclosure, metalpillars 56 are embedded in dielectric layer 58, with the top surfaces ofdielectric layers 58 being higher than the top surfaces of metal pillars56. Dielectric layer 58 may be formed of a polymer, which may includePBO, polyimide, or the like.

Referring to FIG. 7, molding material 60 is molded on device dies 52 andthrough-vias 50. The respective step is shown as step 214 in the processflow shown in FIG. 22. Molding material 60 may include a moldingcompound, a molding underfill, an epoxy, or a resin. After the moldingprocess, the top surface of molding material 60 is higher than the topends of metal pillars 56 and through-vias 50. Molding material 60 isfilled into openings 49 (FIG. 6) to contact molding material 44. Inaccordance with some embodiments of the present disclosure, moldingmaterial 44 and molding material 60 are formed of a same type of moldingmaterial. In accordance with alternative embodiments, molding material44 and molding material 60 are formed of different types of moldingmaterials.

Next, a planarization step is performed to planarize molding material60, until through-vias 50 are exposed. The respective step is shown asstep 216 in the process flow shown in FIG. 22. The resulting structureis shown in FIG. 8. Metal pillars 56 of device dies 52 are also exposedas a result of the planarization. Due to the planarization, the topsurfaces of through-vias 50 are substantially level (coplanar) with thetop surfaces of metal pillars 56, and are substantially level (coplanar)with the top surface of molding material 60.

Referring to FIG. 9, one or more layers of dielectric layers 62 and therespective RDLs 64 are formed over molding material 60, through-vias 50,and metal pillars 56. The respective step is shown as step 218 in theprocess flow shown in FIG. 22. In accordance with some embodiments ofthe present disclosure, dielectric layers 62 are formed of a polymer(s)such as PBO, polyimide, or the like. In accordance with alternativeembodiments of the present disclosure, dielectric layers 62 are formedof an inorganic dielectric material(s) such as silicon nitride, siliconoxide, silicon oxynitride, or the like.

RDLs 64 are formed to electrically couple to metal pillars 56 andthrough-vias 50. RDLs 64 may also electrically interconnect metalpillars 56, through-vias 50, and metal pillars 40 with each other. RDLs64 may include metal traces (metal lines) and vias underlying andconnected to the metal traces. In accordance with some embodiments ofthe present disclosure, RDLs 64 are formed through plating processes,wherein each of RDLs 64 includes a seed layer (not shown) and a platedmetallic material over the seed layer. The seed layer and the platedmetallic material may be formed of the same material or differentmaterials.

During the formation of RDLs 64, dielectric layers 62 are also patternedto form via openings, and upper-level RDLs 64 extend into the viaopenings to contact lower-level RDLs 64 or metal pillars 56. At the sametime the via openings are formed, some portions of dielectric layers 62are also removed to form openings 66 in dielectric layers 62. Theformation of via openings and openings 66 may be performed using a samelithography mask and same lithography processes. Openings 66 may form agrid, with the remaining portions of dielectric layers 62 being in theregions defined by the grid. Molding material 60 is thus exposed throughopenings 66.

FIG. 10 illustrates the formation of electrical connectors 68 inaccordance with some exemplary embodiments of the present disclosure.The respective step is shown as step 224 in the process flow shown inFIG. 22. Electrical connectors 68 are electrically coupled to RDLs 64,metal pillars 40 and 56, and/or through-vias 50. The formation ofelectrical connectors 68 may include placing solder balls over RDLs 64and then reflowing the solder balls. In accordance with alternativeembodiments of the present disclosure, the formation of electricalconnectors 68 includes performing a plating step to form solder regionsover RDLs 64 and then reflowing the solder regions. Electricalconnectors 68 may also include metal pillars, or metal pillars andsolder caps, which may also be formed through plating. Throughout thedescription, the combined structure including device dies 52,through-vias 50, molding material 60, RDLs 64, and dielectric layers 62will be referred to as package 70, which is also a composite wafer.

In accordance with some embodiments of the present disclosure, width W1of opening 49 (also refer to FIG. 4) is in the range between about 100μm and about 300 μm. Width W2 of openings 66 is in the range betweenabout 100 μm and about 300 μm. Width W2 may be greater than or equal towidth W1. Width W3 of the saw-line is in the range between about 30 μmand about 40 μm.

Next, package 70 is de-bonded from carrier 30. In accordance with someexemplary de-boding process, a dicing tape (not shown) is attached topackage 72 to protect electrical connectors 68. The de-bonding ofpackage 70 from carrier 30 is performed, for example, by projecting a UVlight or a laser on adhesive layer 32. For example, when adhesive layer32 is formed of LTHC, the heat generated from the light or laser causesthe LTHC to be decomposed, and hence carrier 30 is detached from package72. In a subsequent step, die-saw is performed to saw package 70 intodiscrete packages 72. The respective step is also shown as step 224 inthe process flow shown in FIG. 22.

FIG. 11 illustrates a resulting discrete package 72. Package 72 includesdevice dies 36 at a lower level, and device dies 52 at an upper level.Device dies 36 and 52 are electrically interconnected through RDLs 48and 64 and through-vias 50 to form a multi-stacking package 72.Dielectric layers 46, which may be polymer layers, are formed betweenlower-level die(s) 36 and upper-level dies 52. Lower-level dies 36 aremolded in molding material 44, and upper-level dies 52 are molded inmolding material 60. Molding material 60 extends down, with a portion ofmolding material 60 being coplanar with dielectric layers 46.

FIG. 12 illustrates a top view of a portion of discrete package 72,wherein the top view is obtained at the level of dielectric layers 46.As shown in FIG. 12, a portion of molding material 60 (referred to as aring portion hereinafter) encircles dielectric layers 46. Also, edges62A of dielectric layers 62 are misaligned with the respective edges ofmolding materials 44 and 60, and are recessed more toward the center ofpackage 72.

In accordance with some embodiments of the present disclosure, edge 62Aof dielectric layers 62 is recessed from edge 60A of molding material 60(and edge 44A of molding material 44) by recessing distance D1, whichmay be in the range between about 30 μm and about 130 μm. The width ofthe ring portion of molding material 60 is equal to recessing distanceD2, which is the recessing distance of edge 46A of dielectric layers 46recessed from edge 60A of molding material 60. Recessing distance D2 mayalso be in the range between about 30 μm and about 130 μm.

Furthermore, the bottom surface of the ring portion of molding material60 is coplanar with the bottom surface of dielectric layers 46, as shownin FIG. 11, and is in contact with the top surface of molding material44 to form interface 80. Regardless of whether molding materials 44 and60 are formed of a same material or different molding materials,interface 80 is distinguishable due to the planarization of moldingmaterial 44. For example, FIG. 13 illustrates a schematic magnified viewof a portion of package 72 in region 74 (FIG. 11). Molding material 44may include fillers 76A in polymer 78A. Molding material 60 may includefillers 76B in polymer 78B. Fillers 76A and 76B may be formed of silica,aluminum oxide, aluminum nitride, silicon carbide, or the like, and thematerial of fillers 76A may be the same or different from the materialof fillers 76B. Furthermore, fillers 76A and 76B may have sphericalshapes. Due to the planarization of molding material 44, fillers 76A arealso grinded, and the top portions of some fillers 76A are removed.Accordingly, some top portions of fillers 76A may have planar topsurfaces coplanar with interface 80, with these fillers 76A having roundlower parts. On the other hand, some fillers 76B that contact interface80 have rounded bottom ends coplanar with interface 80. Accordingly,interface 80 is distinguishable through the shapes of fillers 76A and76B.

FIGS. 14 through 16 illustrate the cross-sectional views of intermediatestages in the formation of a multi-stacking package in accordance withalternative embodiments of the present disclosure. Unless specifiedotherwise, the materials and the formation methods of the components inthese embodiments are essentially the same as the like components, whichare denoted by like reference numerals in the embodiments shown in FIGS.1 through 13. The details regarding the formation process and thematerials of the components shown in FIGS. 14 through 16 (and also FIGS.17 through 21) may thus be found in the discussion of the embodimentsshown in FIGS. 1 through 13.

The initial steps of these embodiments are essentially the same as shownin FIGS. 1 through 8. Next, as shown in FIG. 14, dielectric layers 62and RDLs 64 are formed. The formation process is similar to the processin FIG. 9, except that when via openings are formed in dielectric layers62, no openings are formed between device dies 52. Alternatively stated,openings 66 as shown in FIG. 9 are not formed in accordance with theseembodiments. Next, as shown in FIG. 15, electrical connectors 68 areformed, and a die-saw is performed to separate package 70 into packages72. A resulting discrete package 72 is shown in FIG. 16. The package 72in FIG. 16 is similar to the package 72 shown in FIG. 11, except thatthe edges of dielectric layers 62 are vertically aligned to (co-terminuswith and it the same vertical plane as) the respective edges of moldingmaterials 44 and 60.

FIGS. 17 and 18 illustrate the cross-sectional views of intermediatestages in the formation of a multi-stacking package in accordance withyet alternative embodiments of the present disclosure. The initial stepsof these embodiments are essentially the same as shown in FIGS. 1through 9. Next, as shown in FIG. 17, liquid molding compound 74 isapplied to protect package 70, wherein the lower parts of electricalconnectors 68 are molded in liquid molding compound 74. The respectivestep is shown as step 222 in the process flow shown in FIG. 22, whereinthe dashed box indicates step 222 may be performed or skipped indifferent embodiments. The molding process includes applying liquidmolding compound 74, and pressing liquid molding compound 74 using arelease film (not shown), so that the top parts of electrical connectors68 are pressed into the release film, and the excess liquid moldingcompound 74 is squeezed away from package 72 by the release film. Liquidmolding compound 74 is then cured. The release film is then removed,leaving the structure in FIG. 17. The cured liquid molding compound 74is referred to as molding material 74 hereinafter. Molding materials 60and 74 may be formed of a same molding material, or may be formed ofdifferent molding materials.

Package 70 is then de-bonded from carrier 30, and is sawed. Theresulting discrete package 72 is shown in FIG. 18. In package 72, inaddition to the ring portion (a full ring) of molding material 60 thatencircles dielectric layers 46, molding material 74 also has a ringportion (a full ring) encircling dielectric layers 62. The bottomsurface of molding material 74 contacts the top surface of moldingmaterial 60 to form interface 76. Interface 76 is distinguishable sincemolding material 60 is grinded or polished, and hence the fillers inmolding material 60 will also be polished to have planar top surfacescoplanar with interface 76. The distinguishable features of interface 76are similar to what is shown in FIG. 13.

FIGS. 19 through 21 illustrate the cross-sectional views of intermediatestages in the formation of a multi-stacking package in accordance withalternative embodiments of the present disclosure. The initial steps ofthese embodiments are essentially the same as shown in FIGS. 1 through9. Next, as shown in FIG. 19, a partial cut is performed to cut (forexample, through sawing) into molding material 60, and hence formingtrench 78 in molding material 60. The respective step is shown as step220 in the process flow shown in FIG. 22. Trench 78 may be aligned tothe center of the respective overlaying trench 66. The bottom of trench78 may be at an intermediate level between the top surface of the topdielectric layer 46 and the bottom surface of the bottom dielectriclayer 46. In accordance with some exemplary embodiments, width W4 oftrench 78 is in the range between about 50 μm and about 80 μm. The depthof trench 78 may be in the range between about 50 μm and about 80 μm.Again, trenches 78 may form a grid, with dielectric layers 46 in thegrid openings defined by the grid.

FIG. 20 illustrates the formation of molding material 74, for example,through applying and curing a liquid molding compound. Molding material74 fills trench 78 (FIG. 19) and contacts the sidewalls and the topsurface of molding material 60.

Package 70 is then de-bonded from carrier 30, and is sawed. Theresulting package 72 sawed from package 70 is shown in FIG. 21. In thepackage 72 according to these embodiments, the portions of moldingmaterial 74 filled into trenches 78 (FIG. 19) form a ring encirclingportions of molding material 60. Furthermore, molding material 74 alsohas a ring portion encircling dielectric layers 62 and at least some topportions of dielectric layers 46.

The embodiments of the present disclosure have some advantageousfeatures. By patterning the polymer layers between lower-level dies andupper-level dies, the polymer layers are separated into discreteportions during the manufacturing process, and hence the stress causedto package by the polymer layers is reduced. The space that willotherwise be occupied by the polymer layers are hence occupied bymolding compound, which includes fillers, and hence have a smallereffect in causing warpage in the package than large polymer areas.

In accordance with some embodiments of the present disclosure, a packageincludes a first molding material, a lower-level device die in the firstmolding material, a dielectric layer over the lower-level device die andthe first molding material, and a plurality of redistribution linesextending into the first dielectric layer to electrically couple to thelower-level device die. The package further includes an upper-leveldevice die over the dielectric layer, and a second molding materialmolding the upper-level device die therein. A bottom surface of aportion of the second molding material contacts a top surface of thefirst molding material.

In accordance with alternative embodiments of the present disclosure, apackage includes a first molding material, a lower-level device die inthe first molding material, a first polymer layer over the lower-leveldevice die and the first molding material, and a first plurality ofredistribution lines extending into the first polymer layer toelectrically couple to the lower-level device die. An upper-level devicedie is disposed over the first polymer layer. A second molding materialmolds the upper-level device die therein, wherein a first edge of thefirst molding material and a second edge of the second molding materialare in a same plane to form an edge of the package. A portion of thesecond molding material includes the second edge and a third edgeopposite to each other, with the third edge contacting the first polymerlayer. A through-via is disposed in the second molding material, whereinthe through-via and one of the first plurality of redistribution lineselectrically couple the lower-level device die to the upper-level devicedie.

In accordance with alternative embodiments of the present disclosure, amethod includes molding a lower-level device die in a first moldingmaterial, planarizing the first molding material to expose thelower-level device die, forming a first polymer layer over the firstmolding material, patterning the first polymer layer to form a firsttrench, placing an upper-level device die over the first polymer layer,and molding the upper-level device die in a second molding material,wherein the second molding material fills the first trench to contactthe first molding material. The second molding material is planarized toexpose the upper-level device die.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: encapsulating a lower-leveldevice die in a first encapsulating material; forming a redistributionstructure comprising: a dielectric layer; and a plurality ofredistribution lines extending into the dielectric layer; patterning theredistribution structure to reveal the first encapsulating material;placing an upper-level device die over the redistribution structure; andencapsulating the upper-level device die in a second encapsulatingmaterial.